One‐dimensional Semiconducting Metal Oxides: Synthesis, Characterization and Gas Sensors Application

Abstract

One-dimensional (1-D) structure semiconducting metal oxides, such as nanorods, nanowires, and nanotubes have attracted scientists worldwide because they have many potential applications, including catalysts, photocatalysts, photoemission, solar cells, nanogenerators, field emission, lasers, building block in nanoelectronic devices, and gas sensors. Additionally, 1-D materials have two quantum-confined directions while still leaving one unconfined direction for electrical conduction, making them suitable for resistive-type gas sensor applications. The resistive-type gas sensors operate based on the change in electrical conductance of sensing materials upon gaseous molecules exposures. One-dimensional structures of various semiconducting metal oxides have been fabricated for gas sensors and the applications include CuO, Sn0 2 , Ti0 2 , ZnO and W0 3 . The 1-D structured materials can be fabricated by a "top-down" approach, using advanced nanolithographic techniques, such as electron-beam, focusedion-beam writing, proximal probe patterning, X-ray or extreme-UV, and nanoscale spacer lithography. Otherwise they can be fabricated by "bottom-up" routes, including catalytic growth process, thermal evaporation, thermal chemical vapor deposition (CVD), template assisted route, and hydrothermal or solution methods. This chapter provides brief information about the synthesis and characterization of 1-D semiconducting metal oxides. In addition, the gas sensors application of 1-D materials is introduced in terms of sensitivity, selectivity, response time, recovery time, and sensing mechanisms.

Iron Oxide Nanoparticles for Next Generation Gas Sensors

“…The different synthetic methods are briefly discussed [3,4], and all kinds of Fe 2 O 3 and Fe 3 O 4 oxide nano-, and microstructures were reduced by H 2 to form a variety of the Fe metal nano-, and microstructures. It concludes vapor phase growth, vapor-liquid-solid mechanism, vapor solid mechanism, solution phase growth, template free synthesis etc for the controlled and shaped synthesis of micro/nanoscale metal and oxide systems.…”

“…They involve in gas adsorption in physisorption and chemisorption. In these processes, the most commonly observed chemisorbed species on metal oxide surface operating in air is O to O −2 [3,4]. Reducing gases interact with metal oxides through either direct chemisorption or a surface state associated with the adsorbed oxygen p-or n-type materials.…”

“…Gas sensors operating based on chemisorption have nominal operating temperatures more than 300 up to 600 or less than 1000°C, e.g. oxygen sensors [3][4][5]. Therefore, the further investigations of reduction, oxidation, and dissociation of gases are very crucial to improve gas sensors significantly.…”

“…In the various approach ways, Fe oxide particles with the very wide diversity of nanostructures and microstructures can be synthesized by various chemical and physical methods [58,70]. It is well known that the α-, β-, and γ-Fe 2 O 3 oxides were used for gas sensors for detection of ethanol [3,4,70]. In the research approach methods, large and polyhedral α-Fe 2 O 3 oxide nanoparticles in the size ranges of 1-5 μm, and 1-10 μm can be simply synthesized by modified polyol methods with the additions of a certain amount of NaBH 4 , NaOH, NH 4 OH, and other industrial chemicals.…”

“…Among them, Sn and Fe oxides have proven superior for practical application as gas sensing materials films [9,16,17,44]. Additionally, there are various perovskites with the general formula ABO 3 , typically as SrTiO 3 and SrTi (1-x) Fe x O 3 that are promising candidates for high-temperature sensors to detect NO 2 , CO, and CH 4 , respectively [6][7][8]. However, gas sensors must satisfy the strict requirements and standards of sensitivity, selectivity, and stability [1][2][3][4][5][6][7][8][9].…”